Metal oxide semiconductor (MOS) varactors are widely used in radio frequency (RF) applications. In general, it is desirable for varactors to have a large tuning range to provide better functionality. However, conventional varactors typically employ gate stack structures for N-channel metal-oxide-semiconductor (NMOS) devices with relatively small tuning ranges.
Therefore, a novel gate stack structure and method of manufacturing the same are required to increase the tuning range of the MOS varactor.